1. Field of the Invention
The present invention relates to a hard disk drive, and more particularly, to an actuator of a hard disk drive having a structure to reinforce a coupling force between an actuator arm and a molding portion.
2. Description of the Related Art
A hard disk drive (HDD) is one of auxiliary memory devices to read out and record data from and on a magnetic disk by using a magnetic head.
FIG. 1 is a perspective view showing a conventional hard disk drive. Referring to the drawing, a conventional hard disk drive includes a housing 10, a magnetic disk (hard disk) 20 which is a recording medium installed in the housing 10, a spindle motor 30 installed on a base plate 11 of the housing 10 to rotate the disk 20, and an actuator 40 having a magnetic head for recording/reading out data.
The housing 10 is installed in a main body of a computer and includes the base plate 11 supporting the spindle motor 30 and the actuator 40, and a cover plate 12 coupled to the base plate 11 enclosing and protecting the disk 20. The housing 10 is typically manufactured of a stainless and/or aluminum material.
The disk 20 is a recording medium for data recording and a single or a plurality of disks are installed at predetermined distances from each other and capable of being rotated by the spindle motor 30. A parking (landing) zone 21 is provided at the inner circumferential side of the disk 20, where a slider 42 with a magnetic head (not shown) is accommodated when the power is turned off. A data zone 22 where data is stored is provided outside the landing zone 21.
The actuator 40 includes an actuator arm 46 capable of pivoting around a pivot shaft 47 on the base plate 11, the slider 42, and a suspension 44 installed at one end portion of the actuator arm 46. The suspension elastically biases the slider 42 toward the surface of the disk 20. A voice coil motor 48 pivots the actuator arm 46.
In the conventional hard disk drive having the above structure, when the power is turned off, the slider 42 is accommodated in the landing zone 21 of the disk 20 by the elastic force of the suspension 44. When the power is turned on, the disk 20 starts to rotate and then lift is generated by air pressure. Accordingly, the slider 42 is lifted. The slider 42 is moved to the data zone 22 of the disk 20 by the pivot of the actuator arm 46 of the actuator 40. The slider 42 maintains a height that balances the upward lift caused by the rotation of the disk 20 and the downward elastic force provided by the suspension 44. Thus, the magnetic head mounted on the slider 42 records and reads out data with respect to the disk 20 while maintaining a predetermined distance from the rotating disk 20.
In the hard disk drive, as described above, a single or a plurality of disks are installed. Conventionally, four or more disks are installed in the hard disk drive to increase data storage capacity. Since the surface recording density of a disk has recently increased sharply, one or two disks can store a sufficient amount of data. In particular, a hard disk drive in a method of using a single disk and recording data on one or both side surfaces thereof has been researched and developed. In this case, since only one or two magnetic heads are needed, the actuator has one or two actuator arms and a low profile actuator having a relatively low height can be used.
FIG. 2 is a perspective view showing a conventional low profile actuator. FIG. 3 is an enlarged sectional view taken along line A-A of FIG. 2.
Referring to FIGS. 2 and 3, a conventional low profile actuator 50 has an actuator arm 56 where a pivot hole 57 is provided in the middle portion thereof. A suspension 54 that elastically biases the slider 52 toward the surface of a disk (not shown) is installed at one end portion of the actuator arm 56. A coil 58a of a voice coil motor 58 is coupled to the other end portion of the actuator arm 56. A magnet 58b of the voice coil motor 58 is installed above and under the coil 58a a predetermined distance from the coil 58a. 
The actuator arm 56 is manufactured by press processing and/or stamp processing a metal material, for example, an aluminum plate. The coil 58a is coupled to the other end portion of the actuator arm 56 by interposing a molding portion 59 therebetween. The molding portion 59 is formed by injecting plastic resin between the coil 58a and the actuator arm 56 so that the coil 58a is fixedly coupled to the actuator arm 56 by an adhesive force between the molding portion 59 and each of the coil 58a and the actuator arm 56.
The actuator 50 having the above structure is controlled by a servo control system (not shown) and moves in a direction according to Fleming's left hand rule by the interaction between current input to the coil 58a and a magnetic field formed by the magnet 58b. The actuator 50 pivots according to the direction of the current applied to the coil 58a by the servo control system. Rapid changes in the current result in rapid movement of the magnetic head 51, which is an important factor for determining a seek time of the hard disk drive. For better performance, it is advantageous to generate a strong force (torque) by applying sufficient current to create a high intensity magnetic field.
During hard disk drive operation, the actuator constantly pivots and changes direction to appear to move the magnetic head 51 almost instantaneously. The repetitive motion causes vibration having a variety of frequencies and amplitude. This vibration is a factor for vibrating the magnetic head 51. When the magnetic head 51 vibrates, a position error signal (PES) increases, which consequently affects the function of the magnetic head 51 performing read/write operations along a track formed on the disk. Since the performance of a hard disk drive can be improved by minimizing the vibration, the dynamic characteristic of each part must be designed to be optimal and the fixed position between the respective parts must be firmly maintained.
In the conventional actuator 50, however, the contact surface between the actuator arm 56 and the molding portion 59 coupling the coil 58a to the actuator arm 56 is simply flat, resulting in a weak coupling strength therebetween. Thus, when vibration is generated at the actuator 50, the molding portion 59 may partially separate from the actuator arm 56. Accordingly, the vibration of the actuator 50 increases and the performance of the magnetic head 51 deteriorates. Also, the molding portion 59 can be detached from the actuator arm 56 by an impact applied when the actuator 50 is manufactured or the hard disk drive is assembled or delivered. As the separation between the molding portion 59 and the actuator arm 56 becomes worse, a resonance frequency of the actuator 50 tends to decrease. When the resonance frequency decreases a range controlled by the servo control system, normal operation of the actuator 50 is not possible. In particular, in the low profile actuator 50, the thickness of the actuator arm 56 is very thin Thus, a contact area between the molding portion 59 and the actuator arm 56 is small so that the above problems can become more severe.
U.S. Pat. No. 5,165,090 discloses a swing type actuator in which a groove is formed at the outer circumferential surface of a coil to increase a bonding strength between the coil and a hold member. However, it is difficult to form a groove at the outer circumferential surface of the coil, which also requires an additional step. This method may be suitable if the hold member is manufactured with thermoplastic resin. However, it is difficult to apply the above method to an arm manufactured with a metal material such as aluminum as described with reference to FIGS. 2 and 3.